Formation mechanism of monodisperse poly(acrylonitrile-co-methyl acrylate) particles by aqueous phase precipitation polymerization

The synthesis of size-controlled monodisperse polymer particles without emulsifiers remains a significant challenge in polymer science. Poly(acrylonitrile-co-methyl acrylate) (poly(AN-co-MA)) spherical particles with excellent monodispersity (PDI < 0.1) were successfully developed via a one-pot polymerization strategy using acrylonitrile (AN) and methyl acrylate (MA). The effects of key parameters, including pH value, monomer concentration, initiator concentration and temperature, on the particle size of monodisperse poly(AN-co-MA) particles were systematically investigated. Furthermore, the formation mechanism of the PAN-based particles was elucidated through a combination of characterization including Scanning Electron Microscope, Transmission Electron Microscope, Dynamic Light Scattering, water contact angle measurements, Fourier Transform Infrared Spectroscopy, Proton Nuclear Magnetic Resonance, Wide-Angle X-Ray Diffraction and Differential Scanning Calorimetry, among others. The results demonstrate that the inherent reactivity difference between AN and MA drives a temporal composition evolution. MA is preferentially incorporated in the early polymerization stage, facilitating nucleation of primary particles, while AN dominates in the later polymerization stage. Thereby, the continuous shift toward AN-rich segments significantly enhances the crystallinity and mechanical rigidity of the particles, which as a result ensures the formation and maintenance of their perfect spherical morphology. Owing to its operational simplicity and high product purity, this method shows great potential for industrial-scale production.